1. Field of the Invention
The invention relates to a manufacturing method of a semiconductor device and, more particularly, to a manufacturing method of a semiconductor device having a gate electrode which is formed on a gate insulative film on a semiconductor substrate and at least a part of which is made of a metal material.
2. Related Background Arts
In recent years, to realize high integration and high speed of an LSI, for example, a gate electrode having a laminate structure including a metal material layer of a high melting point such as tungsten (W) or the like and a polysilicon layer showing conductivity has been being developed. The electrode structure of such a multilayer is an indispensable technique after the future design reference generation of 0.13 xcexcm. It is earnestly being examined to apply it to devices.
A conventional forming method of a gate electrode of a polysilicon-metal multilayer structure including a polysilicon layer and a metal film will now be described hereinbelow with reference to FIGS. 5(a) to 5(c). FIGS. 5(a) to 5(c) are cross sectional step diagrams showing the conventional forming method of the gate electrode having the polysilicon-metal multilayer structure.
First, as shown in FIG. 5(a), a gate oxide film 302 having a film thickness of, for example, 30 xc3x85, a conductive polysilicon film 303 having a film thickness of, for example, 1000 xc3x85 and containing a conductive impurity, a W/WNx laminate film 304 having a film thickness of, for example, 1000 xc3x85 and consisting of tungsten and tungsten nitride, a silicon nitride film (Si3N4) 305 having a film thickness of, for example, 3000 xc3x85, and a photoresist film 306 are sequentially laminated onto a silicon substrate 301. The Si3N4 film 305 plays a role of a reflection preventing film in a photolithography step to the photoresist film 306. A part of the silicon nitride film 305 is used as an etching mask in the subsequent working step of the gate electrode.
Subsequently, as shown in FIG. 5(b), the photoresist film 306 is subjected to a patterning work comprising exposing and developing processes according to a photolithography technique so as to become a predetermined shape (gate electrode shape) which is necessary for working the gate electrode.
A patterned photoresist film 306a is used as an etching mask and the silicon nitride film 305 is subjected to a selective etching process by an RIE (Reactive Ion Etching) method. An etched silicon nitride film 305a is used as an etching mask and in a state where the photoresist film 306a remains on the mask, the lower laminate film 304 and polysilicon film 303 are sequentially subjected to a selective etching process.
Thus, as shown in FIG. 5(c), the Si3N4 film 305a is used as an etching mask and a gate electrode consisting of a W/WNx laminate film 304a and a polysilicon film 303a is formed under the film 305a. According to the RIE method, an organic system sub-product 307 is formed on the side surface of the gate electrode including the Si3N4 film by a reaction between an etching gas and a photoresist material remaining on the etching mask 305a. Since the organic system sub-product 307 is formed on the side surface of the gate electrode, each side surface of the Si3N4 film 305a, W/WNx laminate film 304a, and polysilicon film 303a is not excessively etched but the gate electrode which maintains a vertical shape is formed.
Subsequently, as shown in FIG. 6, the organic system sub-product 307 is removed by an etching dissolution by using a treatment solution containing a hydrogen peroxide solution (H2O2) such as sulfate peroxide solution (sulfate+hydrogen peroxide solution), ammonia peroxide solution (ammonia+hydrogen peroxide solution), or the like, or an interface between the organic system sub-product 307 and the gate electrode is peeled off by using a hydrofluoric acid solution by an etching operation, thereby removing the organic system sub-product 307.
As mentioned above, the gate electrode consisting of the polysilicon film 303a and W/WNx laminate film 304a is formed.
However, the conventional forming method of the gate electrode including the metal layer film has the following problems in the removing step of the organic system sub-product formed on the side surface of the gate electrode.
 less than 1 greater than  In case of removing the organic system sub-product by using the treatment solution containing (H2O2) such as sulfate peroxide solution, ammonia peroxide solution, or the like, there is a problem such that the metal material (W/WNx laminate film) constructing the gate electrode is oxidized by the treatment solution and eluted, a thickness of metal layer film is reduced, and the gate electrode is extinguished. Further, the eluted metal components also become causes of various contamination.
 less than 2 greater than  In case of removing the organic system sub-product by using the hydrofluoric acid solution, if an etching rate of the hydrofluoric acid treatment solution is too high, there is a fear such that the gate oxide film which is exposed from the gate electrode is extinguished at a position below the gate electrode. When the gate oxide film portion is extinguished, this oxide film portion cannot be used as a protective film for ion implantation for a source and a drain after the formation of the gate. When the oxide film portion is extinguished, there is a problem such that the hydrophobic silicon substrate is exposed. When the hydrophobic silicon substrate is exposed, in a cleaning step after the gate electrode was formed, a water droplet of a cleaning liquid is adhered onto the exposed silicon substrate and becomes a cause of occurrence of watermark-shaped dry defectives.
It is, therefore, an object of the invention to provide a novel and improved manufacturing method of a semiconductor device which can prevent an elution of a gate electrode material and prevent an extinction of a gate insulative film.
To accomplish the above object, according to the first aspect of the invention, there is provided a manufacturing method of a semiconductor device in which a gate electrode at least a part of which is made of a metal material is formed on a gate insulative film formed on a semiconductor substrate, comprising the steps of: forming the gate electrode while forming metal system sub-products onto side walls of the gate electrode, by etching a gate electrode layer formed on the semiconductor substrate; oxidizing the metal system sub-products formed on the side walls of the gate electrode; and removing the oxidized metal system sub-products by a solution whose etching rate for the gate insulative film is adjusted to be equal to or less than 10 xc3x85/min.
According to the second aspect of the invention, there is provided a manufacturing method of a semiconductor device in which a gate electrode at least a part of which is made of a metal material is formed on a gate insulative film formed on a semiconductor substrate, comprising the steps of:
sequentially forming the gate insulative film, a gate electrode layer at least a part of which is made of a metal material, and a silicon nitride film or a silicon oxide film onto the semiconductor substrate; etching the silicon nitride film or silicon oxide film into a predetermined shape; forming the gate electrode while forming metal system sub-products onto side walls of the gate electrode, by etching the gate electrode layer with using the silicon nitride film or silicon oxide film etched in the predetermined shape as a mask; oxidizing the metal system sub-products formed on the side walls of the gate electrode; and removing the oxidized metal system sub-products.
The step of removing the oxidized metal system sub-products may be executed by using an ammonium fluoride solution.
In the ammonium fluoride solution, an etching rate for the gate insulative film may be adjusted to be equal to or less than 10 xc3x85/min.
A solvent of the ammonium fluoride solution is, for example, a solvent of a low dielectric constant.
The solvent of the low dielectric constant is a material such as acetic acid or tetrahydrofuran.
The step of removing the oxidized metal system sub-products may be executed by using sulfate.
In the sulfate, an etching rate for the gate insulative film may be adjusted to be equal to or less than 10 xc3x85/min.
It is preferable that the sulfate is a non-hydrolyzed sulfate stock solution.
The step of removing the oxidized metal system sub-products may be executed by using hydrochloric acid.
In the hydrochloric acid, an etching rate for the gate insulative film may be adjusted to be equal to or less than 10 xc3x85/min.
Preferably, the hydrochloric acid is a non-hydrolyzed hydrochloric acid stock solution.
For example, the metal system sub-product is a product which is formed by a reaction of a metal material constructing the gate electrode and an etching material which is used in the etching of the gate electrode layer in the etching step of the gate electrode layer.
The metal system sub-product is, for example, a product containing at least WCl6.
The etching of the gate electrode layer may be executed by a reactive ion etching method.
Preferably, the step of oxidizing the metal system sub-products formed on the side walls of the gate electrode is ashing with using oxygen.
According to the third aspect of the invention, there is provided a manufacturing method of a semiconductor device having a gate electrode which is formed on a gate oxide film on a semiconductor substrate and has a metal material layer, comprising the steps of: depositing a gate electrode layer for the gate electrode onto the gate oxide film; forming a reflection preventing film layer and a photoresist material layer made of an organic material onto the gate electrode layer, respectively; forming a resist mask in a desired shape from the photoresist material layer by a photolithography technique; performing a selective etching process to the reflection preventing film layer by using the resist mask as an etching mask, thereby forming an etching mask corresponding to the resist mask from the reflection preventing film layer; removing the resist mask, thereafter, performing an etching process to remove a portion exposed from the etching mask in the gate electrode layer under the etching mask by using the etching mask obtained from the reflection preventing film layer, and sequentially growing etching protective films of a metal system onto side portions in a remaining portion of the gate electrode layer locating under the etching mask during the etching process in order to protect the side portions from the etching process; oxidizing the metal system protective films; and removing the oxidized protective films from the remaining portion of the gate electrode layer.
The reflection preventing film may be either a silicon nitride film or a silicon oxide film.
The metal system protective films may be removed by using an ammonium fluoride solution.
The metal system protective films may be removed by using a liquid showing strong acid.
The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings.